In recent years, with increased demand for high-performance plastics, lots of polymers of various novel properties have been developed and come on the market. Among them, liquid crystalline resins having characteristic parallel arrangement of molecular chains and showing optical anisotropy, such as liquid crystalline polyester, have received particular attention, because of their excellent moldability and mechanical properties, and their applications have been expanded to mechanical components and electric and electronic components. In particular, such liquid crystalline resins are favorably used for electric and electronic components requiring the high flowability, such as connectors.
Accompanied with recent downsizing and weight reduction of equipment, there has been increasing demand for mechanical components and electric and electronic components having the thin wall thickness and the more complicated shape. Molded products produced by using the liquid crystalline resin compositions are often used in the form of composite molded products with metals. The resin has the greater coefficient of linear expansion than the metal. In the metal composite molded product, this difference in coefficient of linear expansion may cause the resin part to continuously receive a stress and may thereby lead to a possibility that the resin part is damaged. Additionally, a thin-walled composite molded product has a problem that a dielectric breakdown occurs under application of a high voltage and may cause an insulation failure, due to the extreme thinness of the resin part that is responsible for the insulation property.
As a means to decrease the coefficient of linear expansion, a resin composition has been proposed (see, for example, WO 01/40380), which has a synthetic resin with the melt temperature of not lower than 300° C. mixed with a plate-like inorganic filler having a water dispersible pH of 5.5 to 8.0, the amount of eluted alkali of not greater than 30 ppm for Na and not greater than 40 ppm for K, the maximum diameter of not greater than 50 μm, the thickness of not greater than 1.0 μm and the aspect ratio of not less than 20.
As one means to control the amount of deformation of a molded product during heat treatment, a liquid crystalline polymer composition has been proposed (see, for example, JP 4450902 B), which has 100 parts by weight of a liquid crystalline polymer mixed with 5 to 100 parts by weight of a plate-like filler having a ratio (D/W) of not greater than 5, wherein D/W is the ratio of a maximum particle diameter (D) of the plate-like filler to a particle diameter (W) in a direction (y direction) perpendicular to an x direction which is along the direction of the maximum particle diameter, and a rate of W to a particle thickness (H) in a range of 3 to 200.
As another means to control the amount of deformation of a molded product during heat treatment, a liquid crystalline polyester composition has been proposed (see, for example, JP 3111471 B), which has 100 parts by weight of a liquid crystalline polyester mixed with 1 to 200 parts by weight of a mica having a bulk specific gravity of 0.18 to 0.23 and an average particle diameter of 10 to 15 μm.
As yet another means to control the amount of deformation of a molded product during heat treatment, a liquid crystalline resin composition has been proposed (see, for example, JP 4161611 B), which has 100 parts by weight of one or more liquid crystalline resins, which are selected out of liquid crystalline polyesters and liquid crystalline polyester amides, mixed with 5 to 100 parts by weight of a scale-like filler (i) having a number-average particle diameter of 10 to 48 μm, 5 to 100 parts by weight of a fibrous filler (ii) having a number-average fiber length of 10 to 60 μm and lithium stearate or barium stearate (iii). A molded product produced from any of such resin compositions has an improvement in the amount of deformation during heat treatment, but still has problems that the molded product has insufficient resistance to the continuously applied stress, which may cause breakdown at a joint with a metal, and has insufficient dielectric breakdown strength.
Recent size reduction and refinement of molded products requires satisfaction of both the high degrees of creep property and dielectric breakdown strength. The proposed techniques, however, still do not sufficiently satisfy all these requirements. Therefore, it could be helpful to provide a liquid crystalline polyester composition capable of producing a molded product having high creep property and high dielectric breakdown strength.